I figure them loosely into decisions I have that are really borderline, like if I have to choose between two lefty batters facing lefty pitchers or something. I always fact-check their statements as well by clicking the player link, which "usually" has that player's specific stats vs the specific pitcher (if they've faced them before).

Yes - their terminology regarding "lower-tier righty" or "upper tier lefty" is completely random and unreliable. If you're going to do the research, it's highly advisable you look into the specific players' stat-sheets anyway to make the determination which tier they specifically are in. I do find them helpful, though, because it's input based on "something" - and I'm looking for all the input I can get when determining matchups.